In typical power conversion applications, for example, where the conversion is from alternating current (AC) to direct current (DC), feedback information from the DC output load voltage is a required input variable to the power and power factor control process that can be implemented by hardware, software or a combination thereof. Consequently closed loop power control, and power factor control, is dependent upon load voltage and inherent load voltage ripple.
Furthermore known pulse width modulated (PWM) power factor controllers do not limit instantaneous power in a linear manner. If AC input current exceeds an over current threshold, the PWM controller truncates the gate drive pulse width to instantly limit current and protect the power circuit. This discontinuous current limit boundary distorts the AC current draw, which increases the total harmonic distortion (THD) of the AC input current during such current limiting conditions.
Known power factor controllers are fundamentally designed to regulate a fixed DC output voltage, thus behaving as a constant voltage source. The power quality obtained with such controllers is therefore a function of the feedback obtained from the load voltage, and the magnitude of the instantaneous power drawn from the power source is a direct function of the instantaneous power drawn from the load, within the bandwidth of the error amplifier.
Known power factor controllers use an average current mode control, or peak current mode control, of the power converter. These traditional methods require voltage feedback information from the output load voltage as a control input to the power control circuit. Therefore, ripple voltage and other dynamic transients in the load affect the quality of the current drawn from the power source. The compensated voltage feedback amplifier is typically designed to prevent load voltage ripple from modulating the power control circuit, which would increase harmonic distortion. The bandwidth of the amplifier must therefore be low enough to attenuate the second harmonic of the input voltage frequency. High bandwidth control inherently increases harmonic distortion in these traditional power factor controllers.
It is one object of the present invention to provide closed loop power control and power factor control for a single phase power converter that does not require feedback information from the output of the converter.
It is another object of the present invention to provide controlled power conversion with up to exact unity power factor into DC loads, or pulsed DC loads that may dynamically vary in voltage magnitude.
It is another object of the present invention to provide a power factor control method that bounds both AC input current and AC input power as required by the state of the input voltage of AC power source to produce a robust system, with current and power defined, linearly controlled and linearly bounded, unlike traditional PWM controllers.
It is another object of the present invention to provide a power factor control method that results in low total harmonic distortion during current limit mode operation by linearly bounding both AC input power and current, thereby preserving power quality even when the control circuit is in current limit mode.
It is another object of the present invention to provide constant power quality control into a varying output load voltage, with active power factor correction completely independent of the output voltage feedback that is particularly beneficial for applications requiring variable programmable output voltage control, or for systems that desire a constant power draw into partial discharge or full discharge systems where the load power is highly dynamic.